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Proc Natl Acad Sci U S A. 2016 May 17;113(20):5616-21. doi: 10.1073/pnas.1516277113. Epub 2016 May 2.

Cryptic sequence features within the disordered protein p27Kip1 regulate cell cycle signaling.

Author information

1
Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St. Louis, MO 63130;
2
Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105;
3
Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105; Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Sciences Center, Memphis, TN 38163 pappu@wustl.edu richard.kriwacki@stjude.org.
4
Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St. Louis, MO 63130; pappu@wustl.edu richard.kriwacki@stjude.org.

Abstract

Peptide motifs embedded within intrinsically disordered regions (IDRs) of proteins are often the sites of posttranslational modifications that control cell-signaling pathways. How do IDR sequences modulate the functionalities of motifs? We answer this question using the polyampholytic C-terminal IDR of the cell cycle inhibitory protein p27(Kip1) (p27). Phosphorylation of Thr-187 (T187) within the p27 IDR controls entry into S phase of the cell division cycle. Additionally, the conformational properties of polyampholytic sequences are predicted to be influenced by the linear patterning of oppositely charged residues. Therefore, we designed sequence variants of the p27 IDR to alter charge patterning outside the primary substrate motif containing T187. Computer simulations and biophysical measurements confirm predictions regarding the impact of charge patterning on the global dimensions of IDRs. Through functional studies, we uncover cryptic sequence features within the p27 IDR that influence the efficiency of T187 phosphorylation. Specifically, we find a positive correlation between T187 phosphorylation efficiency and the weighted net charge per residue of an auxiliary motif. We also find that accumulation of positive charges within the auxiliary motif can diminish the efficiency of T187 phosphorylation because this increases the likelihood of long-range intra-IDR interactions that involve both the primary and auxiliary motifs and inhibit their contributions to function. Importantly, our findings suggest that the cryptic sequence features of the WT p27 IDR negatively regulate T187 phosphorylation signaling. Our approaches provide a generalizable strategy for uncovering the influence of sequence contexts on the functionalities of primary motifs in other IDRs.

KEYWORDS:

disordered regions; motif; p27

PMID:
27140628
PMCID:
PMC4878473
DOI:
10.1073/pnas.1516277113
[Indexed for MEDLINE]
Free PMC Article

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